The proposed research is a part of the effort being directed to develop a unified model for the mechanical behaviour of the cardiac muscle. A unified model is essential in organising a mechanistic theory that would predict the mechanical performance of the left ventricle as an intact organ. In this perspective, specific experiments on papillary muscle bundle are designed to characterise the Force-Length-Velocity-Time features of the muscle in the stimulated state. The features of the active muscle need also be combined with the passive features to develop a unified constitutive law.